I'd definitely be interested in reading it.
Obviously, it would get a lot more attention if it was the actual mom instead of a stepmom.
But the idea of the son being attracted to the stepmom (or mom) and then finding out her dark secret is interesting. Especially when the son does so with a sense of hesitation, and the stepmom feels devastated for what she's done. But of course, she needs to keep the secret.